Abstract:

Successional patterns of attached estuarine diatoms were investigated
using laboratory model ecosystems. Artificial substrates
of acrylic plastic were exposed to 0, 4, and 10 hours of desiccation
per day. Diatom assemblages that developed under temperatures
normal for Yaquina Bay, Oregon (control ecosystem) were compared
to assemblages that developed at temperatures elevated 10 C (heated
ecosystem).
Continuously submerged substrates were quickly invaded by solitary,
motile and attached diatoms. By the end of the experiment,
filamentous and tube dwelling colonial diatoms had become established
with many motile and epiphytic diatoms interspersed among the colonies.
However, planktonic taxa were the first to settle on the substrates
exposed to 4 and 10 hours of desiccation. These taxa were
gradually replaced in prominence by solitary, motile and attached taxa
that had previously colonized the continuously submerged substrates
and by several species that were tolerant of desiccation and high air
temperatures. Again, filamentous and tube dwelling forms began to
establish colonies at the end of the experiment.
A total of 21,569 diatoms was counted in 42 samples, and 136
species were identified. The most abundant diatoms found in the
control ecosystem included Navicula directa, Thalassiosira no. 1,
Thalassionema nitzschioides, Nitzschia no. 2, and Navicula diserta.
Thalassiosira no. 1, Thalassionema nitzschioides, Nitzschia aerophila,
Nitzschia sigma, and Navicula no. 2 were the most abundant
species in the heated ecosystem. Of these taxa, Navicula directa
and Thalassionema nitzschioides were the most evenly distributed
over the samples. Species diversity was higher in the heated ecosystem
than in the control ecosystem.